Underground labyrinth Ravne is a complex prehistorical network of tunnels and chambers designed and build by the builders of the pyramids. The idea for this medical study was born after thousands of positive testimonies about health improvements by tourists who visit the site for last 11 years. One of the possible explanations for these phenomena was the concentration of beneficial negative ions in the complex, so the research was determined to be held in the chamber with the highest concentration of negative ions and the idea was to measure objective medical parameters in order to explain the effects on the human body according to modern medicine.